The present invention relates to a process for the preparation of a compound of the formula I, which inhibit the enzyme TAFIa (activated thrombin-activatable fibrinolysis inhibitor), and to the novel intermediate compounds used therein.
The enzyme TAFIa is produced for example through thrombin activation from the thrombin-activatable fibrinolysis inhibitor zymogen (TAFI). The enzyme TAFI is also referred to as plasma procarboxypeptidase B, procarboxypeptidase U or procarboxypeptidase R and is a proenzyme similar to carboxypeptidase B (L. Bajzar, Arterioscler. Thromb. Vasc. Biol. 2000, pages 2511-2518).
During formation of a clot, thrombin is generated as the final product of the coagulation cascade and induces conversion of soluble plasma fibrinogen to an insoluble fibrin matrix. At the same time, thrombin activates the endogenous fibrinolysis inhibitor TAFI. Activated TAFI (TAFIa) is thus produced during thrombus formation and lysis from the zymogen TAFI through the action of thrombin; thrombomodulin in a complex with thrombin increases this effect about 1250-fold. TAFIa cleaves basic amino acids at the carboxy end of fibrin fragments. The loss of carboxy-terminal lysines as binding sites for plasminogen then leads to inhibition of fibrinolysis. Efficient inhibitors of TAFIa prevent the loss of these high-affinity lysine binding sites for plasminogen and, in this way, assist endogenous fibrinolysis by plasmin: TAFIa inhibitors have profibrinolytic effects.
In order to maintain hemostasis in the blood, mechanisms which lead to the clotting of blood and to the breaking up of clots have developed; these are in equilibrium. If a disturbed equilibrium favors coagulation, fibrin is produced in larger quantities, so that pathological processes of thrombus formation may lead to serious pathological states in humans.
Just like excessive coagulation may lead to serious pathological states caused by thrombosis, an antithrombotic treatment entails the risk of unwanted bleeding through disturbance of the formation of a necessary hemostatic plug. Inhibition of TAFIa increases endogenous fibrinolysis—without influencing coagulation and platelet aggregation—i.e. the disturbed equilibrium is shifted in favor of fibrinolysis. It is thus possible both to counter the buildup of a clinically relevant thrombus, and to increase the lysis of a pre-existing clot. On the other hand, buildup of a hemostatic plug is not impaired, so that a hemorrhagic diathesis is probably not to be expected (Bouma et al., J. Thrombosis and Haemostasis, 1, 2003, pages 1566-1574).
Inhibitors of TAFIa have already been described in the International Applications WO03/013526 and WO2005/105781. A region-specific synthesis of N-substituted imidazoles from α-amino acids is described by Ning Xi et al; Tetrahedron Letters, Vol. 46, No. 43, 2005, pages 7315-7319.
The synthetic routes used to prepare compounds of formula in the prior art have synthetic strategies with a late introduction of the R1 group. This is shown in Scheme 1 and is highly advantageous for the elucidation of structure-activity-relationships as this strategy allows high diversity at the end of the synthesis. The synthetic routes described are long (7-8 steps) and start from expensive imidazoyl acetic acid 1 towards compound 6 or 7. This strategy necessitates the use of protection and deprotection sequences, thus severely limiting the synthetic efficiency.
